[Initial corrosion of dental casting alloys in the oral environment].

In order to study the initial corrosive changes of dental casting alloys in the mouth, the condition and composition of the proximal surface of the class II inlay were analyzed by the scanning electron microscope (SEM) and the electron probe microanalyser (EPMA). These analyses on the same small areas of the proximal surface were carried out every week for four weeks. The results were compared with the condition and composition of the preplacement in the mouth, and also with the data from former studies. 1. Changes observed in the 70Au-3Pt-3Pd-10Ag-14Cu alloy (Au-alloy) were slight in comparison to the other alloys in this experiment, both on the surface condition and composition. 2. The 12Au-45Ag-20Pd-18Cu alloy (Pd-alloy) appeared to be stable in the mouth, but the changes were greater than that of the Au-alloy. 3. The Au- and the Pd-alloys appeared to be stabler after hardening heat treatment. 4. The greatest change was observed in the 65Ag-22Sn-13Zn alloy. 5. Little change was found in the 72Ni-19Cr-6Si alloy by visual inspection, but the dendritic structure was observed by SEM. 6. Almost all these changes of the alloys in this study showed somewhat greater changes than those observed in the conventional basic immersion tests of alloys.